Cardiac Muscle Action Potential
CARDIAC MUSCLE CELL ACTION POTENTIAL
PHASE 0: DEPOLARIZATION
Sodium rapidly into cell (calcium slowly into cell)
PHASE 1
Sodium channels close
PHASE 2: PLATEAU PHASE
Potassium rapidly out of cell
Calcium slowly into cell
Calcium from extracellular space and sarcoplasmic reticulum = plateau
PHASE 3: RAPID REPOLARIZATION
Calcium channels close
Potassium rapidly out of cell
Potassium and sodium ion positions reversed
PHASE 4: RESTING POTENTIAL
Leaky potassium channels
Sarcolemma impermeable to sodium
Long absolute refractory period in cardiac muscle cells: phase 0 to phase 3
Second action potential cannot be initiated
Protective mechanism against tetanus (state of maximal contraction)